The present invention is directed to new and useful improvements in rotary vacuum drum filters and more particularly to the drainage deck assemblies for such filters.
Rotary vacuum drum filters are well known and are used for example in the pulp and paper industry to filter and wash pulp slurries. These filters generally comprise a cylindrical drum mounted for rotation in a tank containing a slurry solution. A filter media such as a cloth or other permeable material is provided about the drum and is spaced from the drum surface by an appropriate drainage deck assembly mounted on the outer surface of the drum. As the drum is rotated through a filtration cycle a vacuum is maintained inside the drum whereby a filter cake is formed on the surface of the filter media as the drum ascends from the tank while filtrate is drawn into filtrate compartments by the vacuum.
The filter cake is removed from the surface of the filter media by suitable doctoring means as the drum descends into the tank and the vacuum is interrupted by appropriate valve means. The drainage deck functions to space the filter media from the drum surface and usually includes means to direct the filtrate from the filtrate compartments outwardly of the filter through drainage pipes interconnected to the filtrate compartments and the valve means.
In the past many devices have been utilized to form the drainage deck assembly and although suitable for their intended purposes various problems have been encountered in the use thereof. In particular problems are present in providing effective and economical means to prevent rewetting of the dry filter cake from a runback of the filtrate to the cake as the drum rotates through the descending path of the filtration cycle when the vacuum to the filtrate compartments is interrupted.
Prior art vacuum drum rotary filters of the type discussed which disclose structures for both spacing the filter media from the drum surface and for controlling flow of the filtrate are typified by but not limited to U.S. Pat. Nos. 2,793,755; 3,175,691; 3,794,178; 3,837,499 and 3,954,622.
In U.S. Pat. No. 2,793,755 the deck comprises removable pan assemblies and in U.S. Pat. No. 3,794,178 the deck is comprised of premolded elongated plastic members. In U.S. Pat. No. 3,837,499 perforated corrugated plates are used to space the filter media from the drum surface. Other typical drainage assemblies utilizing grid sections are disclosed in U.S. Pat. Nos. 3,175,691 and 3,954,622 wherein spaced and parallel divider elements extend longitudinally across the surface of the drum to form filtrate compartments therebetween. The preformed drainage grid sectors are located in rows between these spaced dividers to complete the filtrate compartment and are held in place by clamping flanges of the divider element.
It is an object of the present invention to provide a novel drainage deck assembly for a rotary vacuum drum filter.
It is a further object to provide a novel drainage deck assembly comprising a plurality of interconnected premolded sections to form a continuous drainage deck and supporting surface for the filter media.
Another object is to provide a drainage deck structure having both novel integral fluid directing means and means for preventing the flowback of filtrate.
A still further object is to provide a novel drainage deck assembly comprised of a plurality of interconnected premolded drainage sections which provide a lightweight assembly of reduced manufacturing and labor costs.